Extreme value computation

ABSTRACT

The method may include providing a plurality of synopsis techniques for determining a plurality of attribute value information indicative of the at least one attribute. The method may include determining a data characteristic describing the plurality of data rows of the current data block. The method may include selecting, based on the determined data characteristic, at least one synopsis technique of the provided plurality of synopsis techniques suitable for generating the plurality of attribute value information for the at least one attribute of the current data block. The method may include determining the plurality of attribute value information for the at least one attribute of the plurality of data rows of the current data block using the at least one selected synopsis technique. The method may include storing the determined plurality of attribute value information for the current data block to be used for query processing against the data table.

BACKGROUND

The present invention relates to the field of digital computer systems,and more specifically, to a method for storing a data table.

Analytical database systems manage very large amounts of data and areoptimized for queries that must read large portions of it. At the sametime, they offer the complete querying power of Structured QueryLanguage (SQL). As such systems do not focus on on-line transactionprocessing (OLTP) load (i.e. involving point queries), the systemstypically do not index each data row but heavily rely on scanperformance. Hence, there is a continuous need to improve scanperformance in analytical database systems.

SUMMARY

According to one embodiment, a method for storing a data table isprovided. The method may include providing a plurality of synopsistechniques for determining a plurality of attribute value informationindicative of the at least one attribute. The method may also includedetermining a data characteristic describing the plurality of data rowsof the current data block. The method may further include selecting,based on the determined data characteristic, at least one synopsistechnique of the provided plurality of synopsis techniques suitable forgenerating the plurality of attribute value information for the at leastone attribute of the current data block. The method may also includedetermining the plurality of attribute value information for the atleast one attribute of the plurality of data rows of the current datablock using the at least one selected synopsis technique. The method mayfurther include storing the determined plurality of attribute valueinformation for the current data block to be used for query processingagainst the data table.

According to another embodiment, a computer system for processing a datatable is provided. The computer system may include one or moreprocessors, one or more computer-readable memories, one or morecomputer-readable tangible storage devices, and program instructionsstored on at least one of the one or more storage devices for executionby at least one of the one or more processors via at least one of theone or more memories, whereby the computer system is capable ofperforming a method. The method may include providing a plurality ofsynopsis techniques for determining a plurality of attribute valueinformation indicative of the at least one attribute. The method mayalso include determining a data characteristic describing the pluralityof data rows of the current data block. The method may further includeselecting, based on the determined data characteristic, at least onesynopsis technique of the provided plurality of synopsis techniquessuitable for generating the plurality of attribute value information forthe at least one attribute of the current data block. The method mayalso include determining the plurality of attribute value informationfor the at least one attribute of the plurality of data rows of thecurrent data block using the at least one selected synopsis technique.The method may further include storing the determined plurality ofattribute value information for the current data block to be used forquery processing against the data table.

According to yet another embodiment, a computer program product forprocessing a data table is provided. The computer program product mayinclude one or more computer-readable storage devices and programinstructions stored on at least one of the one or more tangible storagedevices, the program instructions executable by a processor. Thecomputer program product may include program instructions to provide aplurality of synopsis techniques for determining a plurality ofattribute value information indicative of the at least one attribute.The computer program product may also include program instructions todetermine a data characteristic describing the plurality of data rows ofthe current data block. The computer program product may further includeprogram instructions to select, based on the determined datacharacteristic, at least one synopsis technique of the providedplurality of synopsis techniques suitable for generating the pluralityof attribute value information for the at least one attribute of thecurrent data block. The computer program product may also includeprogram instructions to determine the plurality of attribute valueinformation for the at least one attribute of the plurality of data rowsof the current data block using the at least one selected synopsistechnique. The computer program product may further include programinstructions to store the determined plurality of attribute valueinformation for the current data block to be used for query processingagainst the data table.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

In the following embodiments of the invention are explained in greaterdetail, by way of example only, making reference to the drawings inwhich:

FIG. 1 represents a computerized system, suited for implementing one ormore method steps as involved in the present disclosure.

FIG. 2 is a flowchart of a method for storing a data table.

FIG. 3 is flowchart of a method for determining attribute valueinformation using a histogram technique.

DETAILED DESCRIPTION

The descriptions of the various embodiments of the present inventionhave been presented for purposes of illustration, but are not intendedto be exhaustive or limited to the embodiments disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the describedembodiments. The terminology used herein was chosen to best explain theprinciples of the embodiments, the practical application or technicalimprovement over technologies found in the marketplace, or to enableothers of ordinary skill in the art to understand the embodimentsdisclosed herein.

The present method may have the advantage of reducing the false positiverates caused by gaps in the value distribution of attributes with fewdistinct values (e.g. false positive: data block is accessed butcontains no rows matching the query predicate). A gap is a range ofvalues of the attribute, whereby the attribute of a given data block hasno value within the gap.

The present method may be a key performance enabler for analyticaldatabase systems, as it may massively save disk input/output (I/O) andcentral processing unit (CPU) resources.

The present method may be repeated for each data block of the datatable. This may result in each data block of the data table beingassociated with an entry that contains the respective attribute valueinformation.

The attribute value information may be descriptive of the attribute.Using the attribute value information a preselection of data blocks ofthe data table may be performed before scanning the preselected datablocks. The attribute value information may comprise information ormetadata on the attribute that allows such a preselection. In oneexample, the attribute value information may comprise at least one ofminimum attribute value of the attribute in the first data block andmaximum attribute value of the attribute of the first data block.

For example, the maximum and the minimum attribute values define a firstrange of values of the attribute in a respective first data block. Forexample, a received data query may require a second range of values ofthe attribute. The processing of the data query may comprise selectingdata blocks of the data table whose respective first range overlap withthe second range and processing those selected data blocks (that forms ascan list).

The term “data block” as used herein may refer to a logical or physicalstorage unit for storing the data of the data table. The data block maybe the smallest storage unit that is handled by a database managementsystem or an operating system of the computer system.

For example, in the present method when the data is loaded (e.g. in formof data blocks), the present method may be performed on the fly for eachdata block of at least part of the data blocks. The computer system maydetermine the synopsis technique that best fits data characteristics ofeach data block. Thus, this may lead to different data blocks havingdifferent synopsis techniques. For some data blocks, the extremum valuesmay be a good fit. For data blocks with few distinct values, on theother hand, it may be more suitable to store the list of values thatoccur in this particular data block. For yet other data blocks, a smallBloom filter combined with the extremum values may approximate the valuedistribution in the data block best. Other synopsis techniques may beintegrated similarly.

In other words, the present method may, for example, include thefollowing steps when the data is loaded into a data block bN or where adata block is stored:

-   -   i. compute the data required for every synopsis technique;    -   ii. determine the data characteristics within the data block bN;    -   iii. decide on one particular synopsis technique to use for the        data block bN; and    -   iv. when bN is complete, store the data (e.g. the attribute        value information) required for the chosen synopsis technique as        entry associated with bN.

When a query computes the list of data blocks to scan (i.e. the scanlist) using the attribute value information, it may be configured tointerpret that entry of every data block differently. Thus, it firstdetermines the synopsis technique employed for a data block. Then thequery predicates are evaluated against the respective entry according tothe employed technique to decide whether or not the data block must bescanned.

According to one embodiment, the data characteristic includes the numberof distinct values of the attribute. The selecting of the synopsistechnique includes comparing the number of distinct values with apredetermined threshold and selecting the synopsis technique based onthe result of comparison.

This may provide a time saving and simplified method for determining theattribute value information as no extra or complicated calculations arerequired for generating the data characteristics. This may involve thecomparison of two values only. In this way, the present embodiment mayenable an efficient use of the computer system by executing the presentembodiment on a hardware component of the computer system, such as afield-programmable gate array (FPGA).

According to one embodiment, the method further comprises in response todetermining that the number of distinct values is smaller than thepredetermined threshold, selecting an in-list technique of the set ofsynopsis techniques, wherein determining the attribute value informationcomprises providing the attribute value information as the distinctvalues of the attribute.

Having the distinct values as the attribute value information mayfurther increase the processing efficiency of data blocks of the datatable. The number of false positives or unnecessary scanned data blocksmay be reduced.

According to one embodiment, the attribute value information is storedin a memory, wherein the threshold comprises a maximum number of memoryunits. The storage of the attribute value information on a main memorymay have the advantage of speeding up the process of defining the scanlist using the attribute value information. By controlling or tuning thepredefined threshold, the present method may provide a balance betweenthe advantage of using the distinct values and the physical limitationof the memory.

According to one embodiment, in response to determining that the numberof distinct values is higher than the predetermined threshold selectinga bloom filter technique of the set of synopsis techniques, wherebydetermining the attribute value information includes inserting eachvalue of the attribute of the current data block into a bit of a bitvector, whereby the attribute value information comprises at least thebit vector. The bit vector or bit array may provide a morespace-efficient storage of the attribute value information whileenabling to reduce the number of unnecessary scanned data blocks.

The inserting of the attribute value into a bit of the bit vector may beperformed using one or more different hash functions defined, each ofwhich maps or hashes the attribute value to one of the bit vectorpositions. For example, to add an attribute value to the bit vector, theattribute value may be fed to the hash function to get array positionwhere to set the bit representing the occurrence of the attribute value.

According to one embodiment, the attribute value information furtherincludes the extremum values of the attribute. This may further reducethe number of unnecessary data blocks scans.

According to one embodiment, the determining of the attribute valueinformation includes scanning the current data block and identifying afixed number j of first distinct values of the attribute for indicatinga value range of the attribute in the current data block; dividing thevalue range into multiple sub-ranges; and creating a distribution ofbuckets each associated with a respective sub-range of the subranges.The method includes further scanning the current data block and, foreach further current value j+1 of the attribute, determining if a bucketis available, and, if so, marking the bucket as a non-empty bucket andproviding the attribute value information as including the extremumvalues of the attribute in the current data block, the buckets and therange of attribute values in each of the buckets. The distribution ofbuckets may, for example, include a histogram.

This embodiment may enable a more space-efficient storage of theattribute value information in particular in a scenario with a highnumber of distinct values in a large value range of the attribute.

According to one embodiment, the method further includes receiving aquery on the attribute of the data table; determining the number ofempty buckets of the distribution of buckets; comparing the determinednumber with a predetermined maximum number of empty buckets; and basedon the comparison result using one of the distribution of buckets andthe extremum values for, deciding to scan or not to scan the currentdata block for evaluating the query. The advantage of further adding theextremum values to the attribute value information may provide afallback position in case of selectivity issues with the distribution ofbuckets such as a histogram.

According to one embodiment, the set of synopsis techniques includes adefault synopsis technique for providing the attribute value informationas the extremum values of the attribute of the set of data rows of thecurrent data block, the method further including: assigning to eachsynopsis technique of the set of synopsis techniques other than thedefault technique a selection criterion to be fulfilled by values of theattribute in order to use the each synopsis technique; whereby theselecting of the synopsis technique includes in response to determiningthat none of the selection criteria is fulfilled selecting the defaultsynopsis technique. This may ensure that a minimum requirement on thenumber false positives is fulfilled.

According to one embodiment, the method further includes: assigning atag to each technique of the set of synopsis techniques; storing the tagof the selected synopsis technique in association with the attributevalue information; receiving a query on the attribute of the data table;reading the tag for interpreting the attribute value information inaccordance with the selected technique; and using the attribute valueinformation for deciding to scan or not scan the current data block forevaluating the query. This may save processing resources that wouldotherwise be required for a blind analysis of the attribute valueinformation.

According to one embodiment, second data blocks of the data tableinclude respective second set of data rows of the data table. The methodfurther includes repeating steps for each of the second data blocks asthe current data block; grouping the resulting attribute valueinformation of the first and second data blocks based on the respectiveused synopsis technique; assigning to each group a tag indicating thesynopsis technique used for the group; receiving a query on theattribute of the data table; and using the attribute value informationgroup by group by reading the respective tag for interpreting theattribute value information of the group in accordance with the synopsistechnique of the group to determine a scan list of data blocks to bescanned for evaluating the query. This may further save processingresources that would otherwise be required for processing each tag ofthe attribute value information.

According to one embodiment, the method is executed on a hardwarecomponent of a computer system, the hardware component including anFPGA. This may make use of hardware advantages of FPGAs.

According to one embodiment, the determining of the data characteristicis performed using metadata descriptive of the overall structure of thedata table. This may save time of processing data characteristics foreach data block.

According to one embodiment, the set of synopsis techniques includes anin-list technique, a Bloom filter technique and a default technique. Thedefault technique provides the attribute value information as theextremum values of the attribute. The in-list technique provides theattribute value information as the distinct values of the attribute. TheBloom filter provides the attribute value information as a bit vector torepresent the attribute values (as described above). The steps areperformed while scanning row by row the first data block and include:

-   -   assigning a counter to the attribute,    -   for a current scanned row:    -   inserting a value of the attribute of the current row into a bit        of a bit vector,    -   updating the data characteristic whereby the data characteristic        includes the counter and the number of filled bits of the bit        vector;    -   determining if the value of the attribute of the row is a        distinct value,    -   if the value of the attribute of the current row is a distinct        value comparing the counter with a predefined maximum number of        distinct values;    -   in case the counter is smaller than the predefined maximum        number of distinct values saving the distinct value in the        memory, incrementing the counter by a predefined value and, in        case the current row is the last row of the current data block,        selecting the in-list technique,    -   in case the counter is higher than the predefined maximum number        of distinct values, discarding the stored distinct values from        the memory;    -   in case the number of filled bits in the bit vector is smaller        than a predetermined maximum number of bits and in case the        current row is the last row of the current data block, selecting        the bloom filter technique,    -   in case the number of filled bits in the bit vector is higher        than the predetermined maximum number of bits, discarding the        bit vector and selecting the default technique,    -   upon finishing the scanning of the current data block, providing        the attribute value information using the selected technique.

In another example, the set of synopsis techniques further includes ahistogram technique. The provision of the attribute value informationusing the selected technique includes:

-   -   determining the number of gaps in the range of values of the        attribute of the current data block, whereby a gap covers values        of the attribute that are not part of the current data block, in        case the number of gaps is higher than a predetermined maximum        number of gaps further switching from the default technique to        the histogram technique and providing the attribute value        information using the histogram technique.

The extremum values may be calculated on the fly as well, such as whilescanning row by row. This embodiment may provide an efficient on the flyexecution of the present method.

According to one embodiment, the range of values of the attributeincludes sub ranges separated by gaps, whereby each sub-range of thesub-ranges covers values of the attribute that are part of the firstdata block, whereby each gap of the gaps covers values of the attributethat are not part of the current data block, whereby the datacharacteristic includes the number of distinct values and/or the numberof gaps. This may further increase the selection efficiency of the scanlist using the attribute value information.

According to one embodiment, the method further includes, in response todetermining that the range of values is smaller than a predefinedmaximum range of values of the attribute and that the number of gaps issmaller than a predetermined maximum number of gaps, selecting a defaultsynopsis technique of the set of synopsis techniques, wherebydetermining the attribute value information includes providing theattribute value information as including the extremum values of theattribute in the current data block.

FIG. 1 represents a general computerized system, suited for implementingmethod steps as involved in the disclosure.

It will be appreciated that the methods described herein are at leastpartly non-interactive, and automated by way of computerized systems,such as servers or embedded systems. In exemplary embodiments though,the methods described herein can be implemented in a (partly)interactive system. These methods can further be implemented in software112, 122 (including firmware 122), hardware (processor) 105, or acombination thereof. In exemplary embodiments, the methods describedherein are implemented in software, as an executable program, and isexecuted by a special or general-purpose digital computer, such as apersonal computer, workstation, minicomputer, or mainframe computer. Themost general system 100, therefore, includes a general-purpose computer101.

In exemplary embodiments, in terms of hardware architecture, as shown inFIG. 1, the computer 101 includes a processor 105, memory (main memory)110 coupled to a memory controller 115, and one or more I/O devices (orperipherals) 10, 145 that are communicatively coupled via a localinput/output controller 135. The I/O controller 135 can be, but is notlimited to, one or more buses or other wired or wireless connections, asis known in the art. The I/O controller 135 may have additionalelements, which are omitted for simplicity, such as controllers, buffers(caches), drivers, repeaters, and receivers, to enable communications.Further, the local interface may include address, control, and/or dataconnections to enable appropriate communications among theaforementioned components. As described herein the I/O devices 10, 145may generally include any generalized cryptographic card or smart cardknown in the art.

The processor 105 is a hardware device for executing software,particularly that stored in memory 110. The processor 105 can be anycustom made or commercially available processor, a CPU, an auxiliaryprocessor among several processors associated with the computer 101, asemiconductor based microprocessor (in the form of a microchip or chipset), a macroprocessor, or generally any device for executing softwareinstructions.

The memory 110 can include any one or combination of volatile memoryelements (e.g., random access memory (RAM, such as DRAM, SRAM, SDRAM,etc.)) and nonvolatile memory elements (e.g., ROM, erasable programmableread only memory (EPROM), electronically erasable programmable read onlymemory (EEPROM), programmable read only memory (PROM). Note that thememory 110 can have a distributed architecture, where various componentsare situated remote from one another, but can be accessed by theprocessor 105.

The software in memory 110 may include one or more separate programs,each of which comprises an ordered listing of executable instructionsfor implementing logical functions, notably functions involved inembodiments of this invention. In the example of FIG. 1, software in thememory 110 includes instructions 112 (e.g. instructions to managedatabases, such as a database management system). The memory 110 mayfurther comprise a query optimizer. The query optimizer may compriseinstructions (e.g. software instructions that when executed may providea query execution plan for executing a given query).

The software in memory 110 shall also typically include a suitableoperating system (OS) 111. The OS 111 essentially controls the executionof other computer programs, such as possibly software 112 forimplementing methods as described herein.

The methods described herein may be in the form of a source program 112,executable program 112 (object code), script, or any other entitycomprising a set of instructions 112 to be performed. When a sourceprogram, then the program needs to be translated via a compiler,assembler, interpreter, etc., which may or may not be included withinthe memory 110, so as to operate properly in connection with the OS 111.Furthermore, the methods can be written as an object orientedprogramming language, which has classes of data and methods, or aprocedure programming language, which has routines, subroutines, and/orfunctions.

In exemplary embodiments, a conventional keyboard 150 and mouse 155 canbe coupled to the I/O controller 135. Other output devices, such as theI/O devices 145, may include input devices, for example but not limitedto a printer, a scanner, microphone, etc. Finally, the I/O devices 10,145 may further include devices that communicate both inputs andoutputs, for instance but not limited to, a network interface card (NIC)or modulator/demodulator (for accessing other files, devices, systems,or a network), a radio frequency (RF) or other transceiver, a telephonicinterface, a bridge, a router, etc. The I/O devices 10, 145 can be anygeneralized cryptographic card or smart card known in the art. Thesystem 100 can further include a display controller 125 coupled to adisplay 130. In exemplary embodiments, the system 100 can furtherinclude a network interface for coupling to a network 165. The network165 can be an IP-based network for communication between the computer101 and any external server, client, etc. via a broadband connection.The network 165 transmits and receives data between the computer 101 andexternal systems 30, which can be involved to perform part or all of thesteps of the methods discussed herein. In exemplary embodiments, network165 can be a managed IP network administered by a service provider. Thenetwork 165 may be implemented in a wireless fashion, e.g., usingwireless protocols and technologies, such as WiFi, WiMax, etc. Thenetwork 165 can also be a packet-switched network such as a local areanetwork, wide area network, metropolitan area network, Internet network,or other similar type of network environment. The network 165 may be afixed wireless network, a wireless local area network (LAN), a wirelesswide area network (WAN) a personal area network (PAN), a virtual privatenetwork (VPN), intranet or other suitable network system and includesequipment for receiving and transmitting signals.

If the computer 101 is a personal computer (PC), workstation,intelligent device, etc., the software in the memory 110 may furtherinclude a basic input output system (BIOS) 122. The BIOS is a set ofessential software routines that initialize and test hardware atstartup, start the OS 111, and support the transfer of data among thehardware devices. The BIOS is stored in ROM so that the BIOS can beexecuted when the computer 101 is activated.

When the computer 101 is in operation, the processor 105 is configuredto execute software 112 stored within the memory 110, to communicatedata to and from the memory 110, and to generally control operations ofthe computer 101 pursuant to the software. The methods described hereinand the OS 111, in whole or in part, but typically the latter, are readby the processor 105, possibly buffered within the processor 105, andthen executed.

When the systems and methods described herein are implemented insoftware 112, as is shown in FIG. 1, the methods can be stored on anycomputer readable medium, such as storage 120, for use by or inconnection with any computer related system or method. The storage 120may comprise a disk storage such as HDD storage.

The storage 120 may include at least one data table (or data set) 127.For example, the software 112 may receive (automatically or uponrequest) as input the data table 127, or may download the data table 127from storage 120 or memory 110.

The data table 127 may include one or more columns 131A-B, wherein eachcolumn is represented by a respective attribute (e.g. “ID” 131A and“Age” 131B). The rows of the data table 127 may include values of theattributes. The data table 127 may for example include or may be storedon multiple (e.g. contiguous) data blocks b1-bN.

For example, as illustrated in FIG. 1, the data table 127 may be dividedor split or assigned to data blocks b1-bN using the number of rows inthe data table 127.

In another example, the data table 127 may be split or divided based onstorage size such that each data block b1-bN contains or is assigned toone or more storage units (e.g. data pages). The term “storage unit” asused herein is intended to refer to the minimum addressable unit (e.g.by software 112) in order to store the data table 127. The size of astorage unit may be an integer multiple of the size of a disk unit. Thesize of the storage unit may be user defined. For example, each storageunit (e.g. data page) may correspond to a specific number of bytes ofphysical database space on disk (e.g., 4 KB). Other storage units havingdifferent granularities may be addressable or used in order to storedata e.g. in the storage 120. For example, other storage levels mayinclude containers and extents, whereby extents can be defined in termof number of data pages, while a container can be determined in term ofnumber of extents.

The rows of each data block e.g. b1 of the data table 127 may be storedon contiguous, linked, or indexed disk units (e.g. of storage 120) thatform the corresponding data pages of the data block b1. The term diskunit refers to the minimum addressable unit on storage 120. For example,a disk unit may have a size of 512 bytes. The data blocks b1-bN may ormay not include the same number of data pages.

The term “data table” or data set as used herein refers to a collectionof data that may be presented in tabular form. Each column in the datatable may represent a particular variable or attribute. Each row in thedata table may represent a given member, record, or entry of the datatable.

While FIG. 1 only shows a few attributes and data blocks, it will beappreciated that numerous attributes and/or data blocks may exist or maybe used.

FIG. 2 is a flowchart of a method for storing a data table e.g. datatable 127. The data table has or includes at least one attribute 131A-B.A first data block (e.g. b1) of the data table 127 includes a set ofdata rows of the data table 127. In the example shown in FIG. 1, the setof records or rows of b1 includes rows 211-217.

In step 201, a set of synopsis techniques may be provided fordetermining attribute value information indicative of the attribute131B. The term “technique” as used herein, may refer, for example, toseries or steps or processes (e.g. computer-readable instructions) thatreceive an input and provide an output. For example a technique mayreceive as input a given number of attribute values (e.g. by scanning adata block) for a given attribute and may produce attribute valueinformation that describe the attribute.

The set of synopsis techniques may, for example, be stored in the formof one or more files (e.g. in memory 110) containing an indication ofeach of the synopsis techniques. The set of synopsis techniques may, forexample, be received at the computer system 100 as inputs from a user ofthe computer system. In another example the set of synopsis techniquesmay be generated or selected at the computer system 100 using predefinedtechniques.

In step 203, a data characteristic describing the set of data rows ofthe first data block may be determined. The first data block may be acurrent data block being processed by the present method.

The data characteristic refers to information that identifies orcharacterizes the data table. For example, data characteristic may referto information that identifies or characterizes attribute values of oneor more attributes in the data table. In another example, the data mayrefer to information that identifies or characterizes attribute valuesof all attributes in the data table. For example, the datacharacteristic may include the number of distinct values of theattribute 131B.

In another example, the data characteristic may include metadatadescriptive of the overall structure of the data table (i.e. not onlythe set of records or rows of the current data block but also remainingrecords of the data table are described by the data characteristic).This may enable to detect columns or attributes that are unlikely tobenefit from a given synopsis technique as in the following examples:

-   -   columns (or attributes) which are defined as unique, as primary        key (which implies unique), as distribution column, or as        organizing column are known or likely to contain a huge number        of distinct values. The same holds for system-generated column        values involving a sequence or the auto-increment feature        offered by some systems;    -   monotonously growing or declining attribute values across data        blocks indicate that the corresponding columns contain large        numbers of distinct values;    -   if the same column featured large numbers of distinct values in        the past, this is unlikely to change in future data blocks.        Thus, if this was the case for a column across many data blocks,        the computer system may stop evaluating different synopsis        techniques and use extremum values of the default technique; and    -   the computer system may consult the statistics of the query        optimizer. In many cases they contain an estimate on the number        of distinct column values. If this number is larger than what        typically works well with the discussed heuristics then the        extremum values may be used directly.

The data characteristic may be stored in association with the data table127 and may include an indication (e.g. row numbers of the set ofrecords) of the first data block to which it is associated.

In one example, step 203 (and following steps 205-209) may be performedin response to receiving a query on the data table. The evaluation ofthe query may include the processing of data blocks of the data table,whereby processing the current data block may include step 203. Thisembodiment may provide an efficient use of resources by making use ofprocessing the received query in order to perform the present method.

In another example, steps 203-209 may automatically be performed as soonas the data table is stored in the computer system.

Using the determined data characteristic, at least one synopsistechnique of the synopsis techniques may be selected in step 205. Theselected synopsis technique may be suitable for generating the attributevalue information for the at least one attribute of the first datablock. The attribute value information may be generated for one or moreattributes of the first data block. The one or more attributes may beuser defined or may be part or involved in a condition of a receivedquery on the data table that triggers the steps 203-209. In anotherexample, the synopsis techniques may be selected for attributes of thefirst data block that have a frequency access higher than a minimumaccess frequency threshold. In other words, an attribute which is notfrequently queried or accessed may not be used for determining thesynopsis technique and then the attribute value information. This maysave processing resources such as storage and CPU.

In a further example, the attribute value information may be generatedfor all attributes of the first data block. For each attribute of thefirst data block, a synopsis technique may be selected in accordancewith step 205.

A given synopsis technique may be associated with a selection criterionthat may be defined, such that, when satisfied, the given synopsistechnique may be selected. The selection criterion may be based on thedata characteristic. Using the above example of distinct values, theselection criterion may include “the number of distinct values of agiven attribute is smaller than a first predetermined threshold” and maybe associated with an in-list technique of the set of synopsistechniques. The in-list technique when performed provides or generatesthe attribute value information as the distinct values of the attribute131B. Using the data characteristic that describes the number ofdistinct values of the given attribute, the selection criterion may beevaluated and if satisfied the in-list technique may be selected.

In another example, the selection criterion may include “the number ofdistinct values of a given attribute is higher than a secondpredetermined threshold” and may be associated with a Bloom filtertechnique of the set of synopsis techniques. The Bloom filter technique,when performed, provides or generates the attribute value information byinserting each value of the attribute 131B of the first data block intoa bit of a bit vector, whereby the attribute value information includesat least the bit vector. Using the data characteristic that describesthe number of distinct values of the given attribute, the selectioncriterion may be evaluated and, if satisfied, the Bloom filter techniquemay be selected.

The first and second thresholds may or may not be equal. For example, ifthe first and second thresholds are different and it is determined thatthe number of distinct values of the given attribute is between thefirst and second thresholds, the default technique may be selected andmay be used to generate the attribute value information for the givenattribute.

In a further example, the selection criterion may include “the number ofdistinct values of a given attribute is higher than a thirdpredetermined threshold and the range of values of the given attributeis higher than a predetermined range threshold” and may be associatedwith a histogram technique of the set of synopsis techniques, asdescribed below, with reference to FIG. 3. For example, the thirdthreshold may be higher than the first and second thresholds.

In an alternative example of the selection criterion example, using themetadata descriptive of the overall structure of the data table, a givencolumn or attribute of the data table which is defined as unique, asprimary key (which implies unique), as distribution column, or asorganizing column may be identified. And, the default technique may beselected for this identified attribute. The default technique maygenerate the attribute value information as the extremum values of theattribute in the first data block.

Using the selected synopsis technique, the attribute value informationmay be determined in step 207 for the attribute of the set of data rowsof the first data block.

In one example, the determined attribute value information of step 207may further include the extremum values of the attribute. In otherwords, step 207 may include performing both the selected synopsistechnique and the default technique. This may be advantageous in casethe attribute value information as determined by the selected synopsistechnique may have a low selection efficiency in that only very few datablocks may be skipped (not scanned) when using that information.

In step 209, the attribute value information for the first data blockmay be stored (e.g. in memory 110) in order to be used for queryprocessing against the data table.

The attribute value information may be stored in contiguous storage. Inthis case, the system may add meta-information to the attribute valueinformation. The meta-information denotes the synopsis techniqueemployed for the attribute value information of each data block. Themeta-information may, for example, include a tag (that indicates whichpart of the storage on which the attribute value information is stored)to allow a query to detect the synopsis technique employed for thecurrent data block. The query will read the tag and interpret theattribute value information according to the stated technique. If allattribute value information for an attribute across all data blocksemploy the same synopsis technique, the system can store only a globaltag, thereby making entry-wise tag interpretation unnecessary.

Alternatively, the attribute value information for the same column maybe grouped by their employed synopsis technique. In this case, thetechnique needs to be defined (e.g., in a tag) only once per group. Aquery computing a scan list may evaluate every group of attribute valueinformation for the attribute and unite the scan lists computed on theindividual groups. This can be implemented very efficiently, such as byusing bit vectors for identifying data blocks that need to be scannedwhich can be combined with bit-wise operations that are supported byvectorized processor instructions.

In one example, steps 203-209 may be repeated for each data block of thedata table 127. In another example, steps 203-209 may be performed for apart of the data blocks of the data table (e.g. only for the first datablock). This may for example be useful for test purpose or other purposewhere the full content of the data table may not be required.

For example, a query that is received on the data table and has acondition, the attribute for which the attribute value information hasbeen determined, may be evaluated by first reading the attribute valueinformation and deciding to scan or not to scan the first data block.The condition may be an inequality condition (e.g. smaller, between, orhigher), equality condition, or a prefix search that may bepre-evaluated using the attribute value information so as to only scanthe first data block, if it may contain records that satisfy the query.For that, the stored attribute value information may be tagged orassociated with a tag that indicates the synopsis technique that hasbeen used to generate the attribute value information. This tag may beread to determine which synopsis technique is used and based on thedetermined synopsis technique the attribute value information may beinterpreted or used accordingly. For example, an application 112 that isused to process the query may include switches that enable switchingbetween different selection conditions, whereby each selection conditionis based on and associate to a respective type of attribute valueinformation. Depending on the value of the tag the application may useone of the selection conditions.

Assuming for exemplification purposes that the query includes aninequality search e.g. “AGE=17”. In case the tag of the attribute valueinformation of the first data block indicates that the default techniqueis used then the selection condition to be used may be based on acomparison between the value “17” and the extremum values that are partof the attribute value information (e.g. if value “17” is not within theextremum values the first data block may not be selected for scanning inorder to evaluate the query).

In case the tag of the attribute value information of the first datablock indicates that the in-list technique is used then the selectioncondition to be used may be a comparison between the value “17” and thedistinct values that are stored as the attribute value information (e.g.if the distinct values are different from 17 then the first data blockmay not be selected for scanning in order to evaluate the query).

In case the attribute value information is generated for multiple datablocks of the data table, the attribute value information may be used toselect a scan list of data blocks of multiple data blocks to be scanned.This may prevent unnecessary scanning of data blocks. In this case, alldetermined attribute value information may be grouped based on therespective used synopsis technique. Each group of the determined groupsmay be assigned a tag indicating the synopsis technique used for thegroup in order to generate the attribute value information. This may beadvantageous as, in case of receiving a query on the attribute of thedata table, the attribute value information may be processedgroup-by-group by reading the respective tag for interpreting theattribute value information of the group in accordance with the synopsistechnique of the group to determine a scan list of data blocks to bescanned for evaluating the query. This may avoid reading the tag foreach attribute value information (i.e. for each data block having theattribute value information) which may save processing resources.

FIG. 3 is a flowchart of a method for determining the attribute valueinformation of step 207 using a histogram technique of the synopsistechniques. The histogram technique may be selected among the synopsistechniques as described above.

In step 301, the first data block may be scanned and a fixed number j offirst distinct values of the attribute may be identified. The identifieddistinct values may indicate a value range of the attribute in the firstdata block.

In step 303, the value range may be divided into multiple sub-ranges.The number of sub-ranges may be randomly chosen. In another example, thenumber of sub-ranges may be user defined.

In step 305, a histogram may be created that includes buckets eachassociated with a respective sub-range of the subranges.

In step 307, the first data block may be further scanned and for eachfurther current value j+1 of the attribute it may be determined if abucket is available (e.g. if it belongs to the bucket), and, if so, thebucket may be marked as a non-empty bucket (e.g. assigning a valuedifferent from zero to the non-empty bucket). If a current value isoutside the determined range of values, it may be assigned to the firstor the last bucket depending on whether the value is smaller than thelowest range value or higher than the highest range value of thehistogram.

In step 309, the attribute value information may be provided orgenerated as including the extremum values of the attribute in the firstdata block, the histogram buckets, and the range of attribute values ineach of the histogram buckets. Having both information may be used forprocessing a received query on the attribute of the data table. Forexample, it may be determined if the number of empty buckets of thehistogram is smaller than a predetermined maximum number of emptybuckets and, if so, the histogram buckets may be used for deciding toscan or not to scan the first data block for evaluating the query,otherwise the extremum values may be used instead.

In another example, the attribute value information may be provided orgenerated in step 309 as comprising the histogram buckets and the rangeof attribute values in each of the histogram buckets.

In the following, further details related to the synopsis techniqueswill be described for a given data block bN and attribute c, such asattribute 131B.

The default technique to approximate the extremum values that occur foran attribute (or in a column corresponding to the attribute) of the rowsstored in a data block saves the smallest and largest value of theattribute in the data block. This may be performed if the value range ofthe data block is small and if there are few gaps in the value range(i.e. the number of gaps is smaller than a predefined number of gaps).

Computation: the extremum values may be computed on the fly using up totwo comparisons against each incoming or scanned value. This computationmay also be cheaply implemented in special hardware, such as FPGAs.

Usage: The extremum values may be used by default, unless a differenttechnique is considered to provide higher benefits for query processing.Ranges defined by extremum values can be used for point and rangepredicates. However, range predicates (and in-list predicates as aspecial case for non-consecutive ranges) might return a large number offalse positive results in case the data characteristics described oflarge gaps in the attribute value distribution of the data block.

Alternatively or in addition or to the extremum values, all values ofthe attribute that occur in bN may be stored in an “in-list” data entryassociated with bN. This technique may be performed if the number ofdistinct values of c in bN is low (e.g. lower than the firstpredetermined threshold). In this case, the “in-list” technique may copewith gaps better than the extremum values. Thus, it does not matterwhich values are stored in bN, so that they can be very far from eachother. Moreover, in-lists do not depend on an ordinal scale. They mayreflect the occurring values on a nominal scale, which may circumventthe problems of false positives due to gaps in the value distribution ofthe attribute.

Computation: The in-list may be computed on the fly by memorizing alldistinct values that have occurred so far. This can be done using a hashtable or fixed-size array in main memory 110. As stated above, thein-list technique may be used for a low number of distinct values. Thus,the computer system may impose a fixed limit of k values that limitsboth the required memory during computation and the size of theresulting entry. When the computer system has observed k distinct valuesfor c in bN and yet another value enters (e.g. scanned by) the computersystem thus exceeding k, then the computer system discards the memoryused for computing the in-list and decides not to use the in-listtechnique for bN.

An alternative approach to compute the in-list is to obtain the distinctvalues occurring in bN directly from a dictionary encoding scheme thatcomprises compressed data of bN. The encoding dictionary may be usedthat assigns every attribute value in the data block bN a certain code.Thus, the dictionary may contain all possible values in a data block.The in-lists may also be implemented cheaply in special hardware, suchas FPGAs. All that is required is memory or registers for k values andcomparing every incoming value against each of them.

Usage: If the computation of an in-list not exceeding k distinct valuessucceeds, then the computer system uses the in-list technique for theentry of bN (e.g. for generating the attribute value information of c ofbN and storing them in the entry of bN). It may support point andin-list predicates very efficiently and might also be used for rangepredicates if extremum values of are computed in addition to thein-list.

The in-lists may be used up to a certain size, as they require memoryfor every distinct value. A Bloom filter may provide a space-efficientprobabilistic alternative. Fewer than 10 bits per value may be requiredfor a 1% false positive probability. By dedicating a fixed number ofbits (e.g., 64) in the entry of bN to a small Bloom filter, the valuesof c in bN may be approximated up to a number that is considerablylarger than the limit of the in-list technique. By adding the extremumvalues, the value range of c in bN is further defined, which mayparticularly be useful for range queries.

Combining the extremum values with a small Bloom filter may address gapsin the value range. It may preferably be used for lower numbers ofdistinct values (but more than the limit of the in-list technique), suchas within large min/max ranges of values of c within bN.

On the other hand, if the min/max range of values of c within bN isnarrow and there are few gaps, then the extremum values may be usedalone without the bloom filter.

Computation: A Bloom filter may be constructed on the fly by hashingevery incoming value to a bit in a bit vector. If the employed hashfunctions are not overly complex, then this computation may not imposemuch overhead. A Bloom filter may also be implemented cheaply in specialhardware, such as FPGAs.

If the computer system has pursued the in-list approach for some timeuntil the k+1 value first occurred, the system may fall back to theBloom filter approach by adding the k+1 values to a new Bloom filter andmemorizing the extremum values before discarding the in-list. From thispoint on, the system adds all incoming (scanned) values to the Bloomfilter without keeping track of the individual values, except for thesmallest and largest values.

Usage: if there are too many distinct values for c in bN for the in-listtechnique, the system attempts the Bloom-filter technique instead. Ifnearly all bits of the Bloom filter's bit vector are set, then itsfilter effect degrades, so that the false positive rate may be close tothe false positive rate obtained when using the extremum values alone.In this case, the computer system deletes the Bloom filter and fallsback to the extremum values.

In-lists and Bloom filter technique may be used to approximate adiscrete set of values. In scenarios with a high number of distinctvalues in a large min/max range, histogram buckets may be utilized sincein-lists and Bloom filters may require too much memory for each entry ofa data block, which must be capable of processing very quickly. In orderto improve this situation, histogram buckets can be created to identifyempty value ranges within the extremum values. The value range is thusdivided into subranges, the histogram buckets. For every bucket thesystem records whether it contains values or not.

Computation: the buckets may be computed by memorizing a fixed number jof distinct values to approximate the value range of c in bN. For this,it is possible to exploit the distinct values computed for the in-listtechnique. At the j+1 value, the range between the smallest and largestvalue is divided into buckets and the j+1 known values are assigned totheir bucket, which is marked “non-empty”, and the smallest and largestvalue is kept. Then the j+1 values are deleted. Extra space (e.g. edgehistogram bins or several extra “reserve” value ranges) for valuesoutside the current range may be reserved as well. From this point on,the incoming or scanned values are only used to mark their respectivesubrange as “non-empty.” Finally, the borders of the smallest andlargest bucket are set to the extremum values of c in bN. Adjacent emptybuckets and adjacent non-empty buckets may for example be merged.

Alternatively, only the extremum values of fixed number of n records canbe computed to determine the initial value range. After it has beensubdivided, the n values must be read again in order to distribute themover their buckets.

Up to a maximal number of buckets the buckets can also be computedcheaply in special hardware, such as FPGAs.

Usage: the buckets may be advantageous in particular if a significantfraction of them is empty. If the computer system detects that all (ornearly all) buckets are full, then the histogram buckets may not be veryrestrictive and the extremum values may be used instead. Thus, in thiscase, the computer system deletes the histogram buckets and falls backto the extremum values technique.

Furthermore, utilizing the feedback from querying may prove to be auseful technique. The synopsis techniques, other than the defaulttechnique, may optionally include the extremum values in their generatedattribute value information. The difference between the extremum valuesand the other attribute value information, such as distinct values, maybe in the false positive rate (i.e., in cases a technique is able to useits attribute value information to tell that a data block can be skippedwhere the extremum values could not). However, it depends on the queryworkload of the computer system whether or not the extra efforts of moreadvanced synopsis techniques pay off. Thus, the computer system mayanalyze the effectiveness of the attribute value information over alonger time frame as follows:

-   -   the computer system may count every scan that was able to skip a        data block where the extremum values alone would not have been        able to detect that this data block can be skipped; and    -   the computer system may count every false positive. These are        cases where a data block was scanned in vain, thus the        additional effort did not pay off.

Using these two measures (per data block, per column or per table), thecomputer system may evaluate where the more advanced synopsis techniquesactually improve scan performance. Only in those places, the computersystem may 1) continue to create them and 2) keep them during the nextdata reorganization.

In another example, a computer-implemented method for processing a datatable in a database management system is provided. The data table has atleast a first attribute. The method includes: providing a set ofsynopsis techniques for determining attribute value information; storinga set of data rows in a current data block (e.g. a data block may be aphysical storage unit or a fixed number of records); determining atleast two pieces of attribute value information for the first attributeof the data rows stored in the current data block, each piece ofattribute value information being calculated with a respective synopsistechnique; determining a data characteristic describing the data rowsstored in the current data block; selecting based on the datacharacteristics which one or ones of the at least two pieces ofattribute value information are relevant for the current data block,resulting in selected attribute value information for the current datablock; and storing the selected attribute value information for thecurrent data block for supporting query processing against the datatable.

Aspects of the present invention are described herein with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems), and computer program products according to embodiments of theinvention. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer readable program instructions.

The present invention may be a system, a method, and/or a computerprogram product. The computer program product may include a computerreadable storage medium (or media) having computer readable programinstructions thereon for causing a processor to carry out aspects of thepresent invention.

The computer readable storage medium can be a tangible device that canretain and store instructions for use by an instruction executiondevice. The computer readable storage medium may be, for example, but isnot limited to, an electronic storage device, a magnetic storage device,an optical storage device, an electromagnetic storage device, asemiconductor storage device, or any suitable combination of theforegoing. A non-exhaustive list of more specific examples of thecomputer readable storage medium includes the following: a portablecomputer diskette, a hard disk, a random access memory (RAM), aread-only memory (ROM), an erasable programmable read-only memory (EPROMor Flash memory), a static random access memory (SRAM), a portablecompact disc read-only memory (CD-ROM), a digital versatile disk (DVD),a memory stick, a floppy disk, a mechanically encoded device such aspunch-cards or raised structures in a groove having instructionsrecorded thereon, and any suitable combination of the foregoing. Acomputer readable storage medium, as used herein, is not to be construedas being transitory signals per se, such as radio waves or other freelypropagating electromagnetic waves, electromagnetic waves propagatingthrough a waveguide or other transmission media (e.g., light pulsespassing through a fiber-optic cable), or electrical signals transmittedthrough a wire.

Computer readable program instructions described herein can bedownloaded to respective computing/processing devices from a computerreadable storage medium or to an external computer or external storagedevice via a network, for example, the Internet, a local area network, awide area network and/or a wireless network. The network may comprisecopper transmission cables, optical transmission fibers, wirelesstransmission, routers, firewalls, switches, gateway computers and/oredge servers. A network adapter card or network interface in eachcomputing/processing device receives computer readable programinstructions from the network and forwards the computer readable programinstructions for storage in a computer readable storage medium withinthe respective computing/processing device.

Computer readable program instructions for carrying out operations ofthe present invention may be assembler instructions,instruction-set-architecture (ISA) instructions, machine instructions,machine dependent instructions, microcode, firmware instructions,state-setting data, or either source code or object code written in anycombination of one or more programming languages, including an objectoriented programming language such as Smalltalk, C++ or the like, andconventional procedural programming languages, such as the “C”programming language or similar programming languages. The computerreadable program instructions may execute entirely on the user'scomputer, partly on the user's computer, as a stand-alone softwarepackage, partly on the user's computer and partly on a remote computeror entirely on the remote computer or server. In the latter scenario,the remote computer may be connected to the user's computer through anytype of network, including a local area network (LAN) or a wide areanetwork (WAN), or the connection may be made to an external computer(for example, through the Internet using an Internet Service Provider).In some embodiments, electronic circuitry including, for example,programmable logic circuitry, field-programmable gate arrays (FPGA), orprogrammable logic arrays (PLA) may execute the computer readableprogram instructions by utilizing state information of the computerreadable program instructions to personalize the electronic circuitry,in order to perform aspects of the present invention.

Aspects of the present invention are described herein with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems), and computer program products according to embodiments of theinvention. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer readable program instructions.

These computer readable program instructions may be provided to aprocessor of a general purpose computer, special purpose computer, orother programmable data processing apparatus to produce a machine, suchthat the instructions, which execute via the processor of the computeror other programmable data processing apparatus, create means forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks. These computer readable program instructionsmay also be stored in a computer readable storage medium that can directa computer, a programmable data processing apparatus, and/or otherdevices to function in a particular manner, such that the computerreadable storage medium having instructions stored therein comprises anarticle of manufacture including instructions which implement aspects ofthe function/act specified in the flowchart and/or block diagram blockor blocks.

The computer readable program instructions may also be loaded onto acomputer, other programmable data processing apparatus, or other deviceto cause a series of operational steps to be performed on the computer,other programmable apparatus or other device to produce a computerimplemented process, such that the instructions which execute on thecomputer, other programmable apparatus, or other device implement thefunctions/acts specified in the flowchart and/or block diagram block orblocks.

The flowchart and block diagrams in the Figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods, and computer program products according to variousembodiments of the present invention. In this regard, each block in theflowchart or block diagrams may represent a module, segment, or portionof instructions, which comprises one or more executable instructions forimplementing the specified logical function(s). In some alternativeimplementations, the functions noted in the block may occur out of theorder noted in the figures. For example, two blocks shown in successionmay, in fact, be executed substantially concurrently, or the blocks maysometimes be executed in the reverse order, depending upon thefunctionality involved. It will also be noted that each block of theblock diagrams and/or flowchart illustration, and combinations of blocksin the block diagrams and/or flowchart illustration, can be implementedby special purpose hardware-based systems that perform the specifiedfunctions or acts or carry out combinations of special purpose hardwareand computer instructions.

What is claimed is:
 1. A computer-implemented method for storing a datatable, wherein the data table has at least one attribute, and wherein afirst data block of the data table comprises a set of data rows of thedata table, and wherein a current data block being the first data block,the method comprising: providing a plurality of synopsis techniques fordetermining a plurality of attribute value information indicative of theat least one attribute; determining a data characteristic describing theplurality of data rows of the current data block; selecting, based onthe determined data characteristic, at least one synopsis technique ofthe provided plurality of synopsis techniques suitable for generatingthe plurality of attribute value information for the at least oneattribute of the current data block; determining the plurality ofattribute value information for the at least one attribute of theplurality of data rows of the current data block using the at least oneselected synopsis technique, wherein determining the plurality ofattribute value information further comprises: scanning the current datablock to identify a fixed number j from a plurality of first distinctvalues of the at least one attribute for indicating a value range of theat least one attribute in the current data block; dividing the valuerange into a plurality of sub-ranges; and creating a distribution of aplurality of buckets, wherein each bucket is associated with arespective sub-range of the plurality of sub-ranges; storing thedetermined plurality of attribute value information for the current datablock to be used for query processing against the data table; furtherscanning the current data block; determining a bucket within theplurality of buckets is available for each further current value j+1 ofthe at least one attribute; marking the bucket as a non-empty bucket;providing the plurality of attribute value information as comprising aplurality of extremum values of the at least one attribute in thecurrent data block, the distribution of the plurality of buckets, andthe value range in each of the distribution of the plurality of buckets;receiving a query of the at least one attribute of the data table;determining a plurality of empty buckets within the distribution of theplurality of buckets; comparing the determined plurality of emptybuckets with a predetermined maximum number; and using one of thedistribution of the plurality of buckets and the plurality of extremumvalues to decide to scan or not to scan the current data block forevaluating the received query based on the compared plurality of emptybuckets.
 2. The method of claim 1, wherein the data characteristiccomprises a plurality of distinct values of the at least one attribute,and wherein selecting the at least one synopsis technique furthercomprises: comparing the plurality of distinct values with apredetermined threshold; and selecting the at least one synopsistechnique based on a result of comparing the plurality of distinctvalues with the predetermined threshold.
 3. The method of claim 2,further comprising: in response to determining that the plurality ofdistinct values is smaller than the predetermined threshold, selectingan in-list technique of the provided plurality of synopsis techniques,wherein determining the plurality of attribute value informationcomprises providing the plurality of attribute value information as theplurality of distinct values of the at least one attribute.
 4. Themethod of claim 3, wherein the plurality of attribute value informationis stored in a memory, and wherein the predetermined threshold comprisesa maximum number of a plurality of memory units.
 5. The method of claim2, further comprising: in response to determining that the plurality ofdistinct values is higher than the predetermined threshold, selecting abloom filter technique within the provided plurality of synopsistechniques, wherein determining the plurality of attribute valueinformation comprises inserting each value of the at least one attributeof the current data block into a bit of a bit vector, and wherein theplurality of attribute value information comprises at least the bitvector.
 6. The method of claim 5, wherein the plurality of attributevalue information further comprises a plurality of extremum values ofthe at least one attribute.
 7. The method of claim 1, wherein theplurality of synopsis techniques comprising a default synopsis techniquefor providing the plurality of attribute value information as theplurality of extremum values of the at least one attribute of theplurality of data rows of the current data block, and wherein the methodfurther comprises: assigning to each synopsis technique of the pluralityof synopsis techniques, other than the default synopsis technique, aselection criterion to be fulfilled by a plurality of values of the atleast one attribute in order to use each synopsis technique, whereinselecting the at least one synopsis technique comprises, in response todetermining the selection criterion is not fulfilled, selecting thedefault synopsis technique.
 8. The method of claim 1, furthercomprising: assigning a tag to each technique of the plurality ofsynopsis techniques; storing the assigned tag of the at least oneselected synopsis technique in association with the plurality ofattribute value information; receiving a query on the at least oneattribute of the data table; reading the stored tag to interpret theplurality of attribute value information in accordance with the at leastone selected synopsis technique; and using the plurality of attributevalue information for deciding to scan or not scan the current datablock for evaluating the received query.
 9. The method of claim 1,wherein a second plurality of data blocks of the data table comprise arespective second plurality of data rows of the data table, the methodfurther comprising: repeating, for each of the second plurality of datablocks, at least one of providing the plurality of synopsis techniques,determine the data characteristic, selecting at least one synopsistechnique, determining a plurality of attribute value information, andstoring the determined plurality of attribute information; grouping aresulting plurality of attribute value information of the first andsecond data blocks based on a respective at least one synopsistechnique; assigning to each group a tag indicating the at least onesynopsis technique used for the group; receiving a query of the at leastone attribute of the data table; and using the plurality of attributevalue information group-by-group by reading the tag corresponding toeach group for interpreting the plurality of attribute value informationof the group in accordance with the at least one synopsis technique ofthe group to determine a scan list of the plurality of data blocks to bescanned for evaluating the query.
 10. The method of claim 1, wherein themethod is executed on a hardware component of a computer system, andwherein the hardware component comprises a field-programmable gatearray.
 11. The method of claim 1, wherein determining the datacharacteristic is performed using a plurality of metadata descriptive ofan overall structure of the data table.
 12. The method of claim 1,wherein the plurality of synopsis techniques comprises an in-listtechnique, a Bloom filter technique, and a default technique; andwherein providing the plurality of synopsis techniques, determine thedata characteristic, selecting at least one synopsis technique,determining a plurality of attribute value information, and storing thedetermined plurality of attribute information are performed whilescanning, row-by-row, the current data block, and further comprising:assigning a counter to the at least one attribute; for a current scannedrow: inserting a value of the at least one attribute of a current rowinto a bit of a bit vector; updating the determined data characteristic,wherein the determined data characteristic comprises the counter and aplurality of filled bits of the bit vector; determining the value of theat least one attribute of the current row is a distinct value; comparingthe assigned counter with a predefined maximum number of a plurality ofdistinct values; if the counter is smaller than the predefined maximumnumber of the plurality of distinct values, the method furthercomprises: saving the distinct value in a memory storage; incrementingthe assigned counter by a predefined value; and if the current row is alast row of the current data block, selecting the in-list technique; ifthe counter is higher than the predefined maximum number of theplurality of distinct values, the method further comprises: discardingthe stored distinct values from the memory storage; if the plurality offilled bits in the bit vector is smaller than a predetermined maximumnumber of the plurality of bits and if the current row is the last rowof the current data block, selecting the Bloom filter technique; if theplurality of filled bits in the bit vector is higher than thepredetermined maximum number of the plurality of bits; and providing theplurality of attribute value information using the at least one selectedsynopsis technique.
 13. The method of claim 12, further comprising: inresponse to determining the range of the plurality of values is smallerthan a maximum window of the plurality of values of the at least oneattribute and a plurality of gaps is smaller than a predeterminedmaximum number of the plurality of gaps, selecting a default techniqueof the provided plurality of synopsis techniques, wherein determiningthe plurality of attribute value information comprises providing theplurality of attribute value information as a plurality of extremumvalues of the at least one attribute in the current data block.
 14. Themethod of claim 1, wherein a range of a plurality of values of the atleast one attribute comprises a plurality of sub-ranges separated by aplurality of gaps, and wherein each sub-range of the plurality ofsub-ranges covers a second plurality of values of the at least oneattribute that are part of the current data block, and wherein each gapof the plurality of gaps covers a third plurality of values of the atleast one attribute that are not part of the current data block, andwherein the determined data characteristic is selected from a groupconsisting of a plurality of distinct values and the plurality of gaps.